This document discusses the plant pathogen Phytophthora. It is an oomycete, not a true fungus, that causes many diseases in plants. Phytophthora reproduces both sexually, requiring two mating types, and asexually through sporangia and zoospores. It infects a wide range of hosts and causes symptoms like leaf spots, stem cankers, root rot, and top dieback. Phytophthora spreads through splashing water or movement of infected plants and soil. It is active in wet and warm conditions. Detection methods include ELISA tests, culturing on selective media, and PCR tests for specific species.

1. Phytophthora
Diseases
Gary W. Moorman
Penn State
Plant Pathology & Environmental Microbiology

2. Late blight of tomato
(Phytophthora infestans)

4. Phytophthora, Oomycete
not a true fungus
Hyphae
Chlamydospores
Sporangia
Antheridia/oogonia
Zoospores
Cell walls contain cellulose
Usually has 2n chromosomes

5. Oogonium
Antheridium
APS Digital Image Collection

6. Phytophthora, sexual reproduction
A1
+
A2
mating types required

7. Sporangium
20-50 Zoospores per sporangium
APS Digital Image Collection

9. Phytophthora
plant pathogens
soil-borne???
…usually plant-borne
APS Digital Image Collection

10. Sporangium
Asexual
reproduction
Zoospore Release
Sporangium
Germinating oospore
by sporangium
Oospore
Formation
Oospore
germinating
by germ tube
Sporangiophore
and
sporangia
Zoospore
Release
Sporangium
Oogonium &
Antheridium
Sexual
reproduction
A1 & A2
mycelium
Zoospores
Life history and disease cycle of Phytophthora

11. Phytophthora activity
Wet conditions, 65F - 70F
sporangia within 4 hours
Each sporangium > 20 to 50 zoospores
released within 1 hour

12. Phytophthora dispersal
 Short distances
Splash
Wind
 Long distances
Movement of
plants or soil

13. Phytophthora cactorum
P. citrophthora
P. citricola
P. cryptogea
P. drechsleri
P. lateralis
P. megasperma
P. parasitica
P. syringae
P. nicotianae
P. ramorum
…many more
top diebacks, leaf spots, stem cankers

14. Many Phytophthora species have a wide host range:
Phytophthora cinnamomi
infects 900 different species

15. Phytophthora root rot
APS Digital Image Collection

17. Douglas-fir infected with
Phytophthora spp.
APS image
collection

18. Photo: Jennifer Parke, Oregon State University

19. Phytophthora root rot
APS Digital Image Collection

20. Severe root rot

21. Phytophthora cinnamomi on
Ilex glabra ‘Shamrock’

22. Top dieback
APS Digital Image Collection

23. Top dieback
V-shaped dead areas
APS Digital Image Collection

24. Symptoms on camellia
Photos: Oregon Dept. of Agriculture & Cheryl Blomquist, CDFA

25. Symptoms on camellia
Photo: Cheryl Blomquist, CDFA

26. P. ramorum symptoms on Kalmia
Photo: DEFRA

27. Similar symptoms – not Phytophthora
Sun scorch
Gray spot on sun scorched leaves
Photo: Rich Regan, Oregon State University

28. Not Phytophthora
Cercospora on Kalmia
Photo: Peter Angwin, USDA-Forest Service

29. Bleeding
cankers
beech

30. beech

31. Reddish-brown discoloration
cambium area infected with
Phytophthora spp.
Photo by Joseph O'Brien
Bugwood.org image collection

32. Phytophthora on
European beech (Fagus sylvatica)
Phytophthora cactorum
Phytophthora citricola
Phytophthora plurivora
Weiland, Nelson and Hudler. 2010
Plant Disease 94: 1009-1014

33. Taxus

34. APS image collection
Coastal live oak infected with
Phytophthora ramorum

35. Phytophthora ramorum
“bleeding”
Photos: Mike McWilliams, ODF & Bruce Moltzen, Missouri Dept. of Conservation

36. Phytophthora ramorum
Sudden …usually slow
Oak
…many other suscepts
Death …often not lethal

37. APS image collection
Penn State image collection
African violet infected with Phytophthora spp.

38. Hosta infected with
Phytophthora spp.
APS image
collection

39. Lavender infected
with
Phytophthora spp.
APS image
collection

40. Polemonium infected
with
Phytophthora spp.
APS image
collection

41. Catharanthus = annual vinca
infected with
Phytophthora spp.
APS image collection

42. Phytophthora nicotianae
on petunia

43. Phytophthora
detection
Phytophthora species in general:
Antibody test (ELISA)
Semi-selective media
ELISA
Plating
Specific Phytophthora
(P. ramorum)
Nested PCR DNA test
Photo: Natalie Goldberg, New Mexico State University
PCR

44. Phytophthora detection
Baiting:

45. If you collect a sample
 Collect various stages
of symptoms.
 Photo symptoms and
environment.

46. Packaging a sample




DRY paper towel
Double bag and seal
Crush proof box
Sample submission form
outside of bags
 Overnight express
Monday-Thursday

47. Phytophthora ramorum
Sporangia releasing
zoospores
Phytophthora ramorum in culture
Photo: UC Davis & UC Berkeley
Chlamydospores

48. QUESTIONS???